The present invention relates to a variable valve timing control apparatus of an internal combustion engine, which variably controls open/close timing of an intake valve and/or an exhaust valve of the engine via hysteresis brake.
In recent years, there have been proposed and developed various variable valve timing control apparatuses. One such variable valve timing control apparatus has been disclosed in Japanese Patent Provisional Publication No. 2005-299604 (hereinafter is referred to as “JP2005-299604”).
The variable valve timing control apparatus disclosed in JP2005-299604 includes a timing sprocket to which a torque (turning force) is transferred from a crankshaft of an engine, a camshaft relatively rotatably supported within a predetermined angular range with respect to the timing sprocket, a sleeve fixedly connected to the camshaft, and a rotational phase control mechanism (or a relative angular phase control or shift mechanism) provided between the timing sprocket and the sleeve so as to control or shift a rotational phase of the camshaft relative to the timing sprocket in accordance with an engine operation condition.
The rotational phase control mechanism includes a radial direction guide window formed in the timing sprocket, a spiral guide (a spiral guide groove) formed on a surface of a spiral guide disk, a link member having two end portions: a base end acting as a pivot and a top end portion slidably supported in the radial direction guide window so that the top end portion can slide in a radial direction along the radial direction guide window, an engagement portion which is provided at the top end portion of the link member and whose top end (a spherical portion or a semi-spherical protrusion) is engaged with the spiral guide, and a hysteresis brake applying a braking force to the spiral guide disk according to the engine operating condition.
When energizing an electromagnetic coil of the hysteresis brake, an electromagnetic brake acts on the spiral guide disk via a hysteresis member. By this braking action, the engagement portion (the top end portion) of the link member moves or slides in the radial direction along the radial direction guide window while being guided by the spiral guide. The sleeve (also the camshaft) can therefore be rotated relative to the timing sprocket within the predetermined angular range. With this, the open/close timing of the intake valve is variably controlled in accordance with the engine operating condition.